To maximize energy conservation, it is desirable to prevent the loss of heat which escapes through flues such as are found in residential and commercial chimneys, industrial boilers, forced air heating and cooling systems and combustion chambers which vent waste gases. It has been reported that up to 90% of the fuel burned for energy for heating or power purposes can be lost by heat escape through air convection currents moving up and exiting out through improperly damped flues. Similarly, it is desirable to control temperatures on a room-by-room basis in homes and offices which employ forced air heating or cooling systems. Numerous devices have been proposed and utilized to control the flow of hot air, cold air and combustion gases through the positioning of dampers mounted within a flue or stack associated with combustion, heat producing or cold-air producing units.
Dampers which fit within a flue or duct are well known in the heating art. At a relatively simple technological level exist those damper apparatuses in which a damper plate is rotatably mounted on a shaft which extends outwardly of the exterior of the flue to be damped and the damper shaft is rotated manually to open or close the flue. See for example, U.S. Pat. No. 4,413,613 to Dunlap.
A more complex approach is reflected in U.S. Pat. No. 4,046,318 to Ripley which discloses an automatic boiler damper activated by a solenoid valve attached to the pivot axis of a damper that is positioned within a stack utilized to vent a heating system. This solenoid is electrically activated upon the appropriate signal from a thermostat secured to a flue, or stack, immediately over the position of the damper assembly. The damper is provided with a vent hole through which heated stack gases flow in sufficient quantity upwardly from the damper in its closed position to activate the thermostat and signal the damper to move to its open position, thereby venting stack gases out through the stack. Heat is conserved in this manner because the damper is closed when the boiler is not being heated, and cold drafts are simultaneously prevented from entering the stack as a downdraft
U.S. Pat. No. 4,237,855 to Shea discloses a related structure intended to throttle the flue to a bare minimum during the period in which the heat source is on, thereby slowing the escape of heat leaving the heat exchanger (i.e., boiler or furnace) and thereby causing it to retain and utilize more heat than the heat exchanger otherwise could. As illustrated, the heating source is wired in parallel with the activating solenoid that ultimately controls the damper position. When the solenoid is energized it lifts the solenoic draw bar which in turn raises a linkage, thereby indirectly rotating a shaft and attached flue damper.
Other patents disclose improved electrical control systems associated with the use of solenoid-activated flue damper operating mechanisms. Thus, for example, U.S. Pat. No. 4,021,187 to Schulte et al. also discloses a solenoid flue gate device, and a series of relay switches which regulate the energizing and deenergizing of the solenoid. The pull of the solenoid itself is resisted by a spring which restores the flue damper to an open position when the solenoid is deenergized or power is lost through an electrical failure, thus enabling a fail safe condition.
Other efforts have been directed to the use of damper this class of device is U.S. Pat. No. 4,281,638 to Delaney which discloses a solar heating system having a motor connected to a suitable electricity source, the motor rotating a damper blade between an open horizontal position and a fully closed position. The Delaney patent teaches that any well-known damper motor may be utilized, and is essentially directed to an improved motorized damper assembly which is intended to minimize the disadvantageous effects of damper blade warping or improper sealing. Alternatively, U.S. Pat. No. 4,039,123 to Frankel utilizes an electric motor having a rotary output shaft to engage a vane shaft which rotates to adjust to the position of a damper within the heating flue. Similarly, U.S. Pat. No. 4,439,139 to Nelson et al. teaches the use of a furnace stack damper control apparatus with a motor connected to the stack damper.
In some applications, it may be particularly desirable to regulate the flow of flue gases and the movement of heat from a combustion chamber by automatic stove dampers or draft inlets that do not require manual attention or the motor driven or solenoid operated attachments as discussed above. Accordingly, it is known in the art to utilize automatic dampers comprising a bimetallic element placed either within or in close proximity to a furnace flue so that the increased temperature of flue gases during combustion deforms the bimetallic element and thereby regulates the position of the damper plate within the flue. Such a damper control is advantageous in that it can be adjusted to produce a graduated response over a range of temperatures and may thereby permit more fine control of combustion and heating.
To this achieve this automatic control approach end, U.S. Pat. No. 4,399,940 to Stiles discloses an automatic stove damper having a temperature responsive element that activates a damper plate. A mechanism for facilitating adjustment of the relative amount of damping provided by the device is disclosed as well as a manual adjustment means which can release the temperature responsive element to quickly shift the damper plate to a fully damped position. The Stiles patent teaches that this feature is desirable in order to enhance the control by the operator of this heating system.
Other types of known devices respond to the movement of air in a system rather than to the temperature of this medium. For example, the Honeywell brand "Sail Switch" is operated by an aluminum sail which can be inserted into an air stream. The movement of air either makes an electrical circuit or breaks a circuit in response to increased air velocity in a forced air duct.
None of the foregoing, however, teach the use of an inexpensive, easily assembled electromechanical device which requires only sufficient electrical power to operate a solenoid associated with a control lever that indirectly regulates movement of a damper for which the motive rotational power is supplied by the movement of hot air, cold air or combustion gases within a flue.